Use of energy to ablate, resect or otherwise cause necrosis in diseased tissue has proven beneficial both to human and to animal health. Microwave ablation and hyperthermia are well-established techniques to heat tumors to the point of necrosis. Larger zones of necrosis and shorter treatment times may be realized by applying larger powers to the antenna. Antennas used to deliver energy at microwave frequencies (300 MHz–300 GHz) to tissue typically require a coaxial cable to feed energy to the antenna. A coaxial antenna is an antenna created from a coaxial transmission line—an electromagnetic structure whereby an inner conductor wire, a dielectric core and outer conductor wire share a common axis. Current coaxial antenna designs use a polymer [e.g., polytetrafluoroethylene (PTFE)] as the dielectric core. Small cable and antenna diameters are required to ensure the procedure is minimally-invasive and safe.
Limitations of the above techniques center on the power rating and diameter of the coaxial cable used to feed the antenna, as well as microwave losses inside the coaxial cable dielectric core. An approximately exponential relationship between cable diameter and power rating exists; that is, as cable diameter decreases, the amount of power that cable may handle without failure decreases exponentially. Losses inside the coaxial cable dielectric core cause heat to be generated when large microwave powers are applied. This causes undue heating of the feeding cable, which causes unwanted necrosis of tissue near the feed cable and is undesirable for patient safety. Thus, the antenna input power is limited by the amount of power the feeding cable may handle without failure and by peripheral heating caused by the feed cable. This, in turn, limits the size of the zone of necrosis obtained in a given time. For this reason, current microwave ablation and hyperthermia antennas are limited in their ability to be operated at high powers and still be safe for percutaneous use.
Therefore, there is a need for a method and device for the delivery of microwave power to tissue which overcomes the above identified disadvantages and limitations of, and which represents an improvement over current coaxial antenna designs. The present disclosure fulfills this need.